► First drive in new TT roadster► Tested here in TTS trim► A proper Boxster rival at last?

The roadster market is in the doldrums. Global sales have almost halved over the past five years, and we may not yet have reached rock bottom.

As a result, conceiving a bespoke standalone roadster makes almost no financial sense anymore. Which is why Porsche twinned Boxster and Cayman, and why the latest drop-top TT has again been derived from the coupé. That's no bad thing: the new TT platform is a good place to start.

While last season's TT featured a steel body over an aluminium suspension, the 2015 vintage fuses a lightweight upper with a chassis made primarily of high-strength steel. That means a lower centre of gravity, improved torsional rigidity and more passenger and luggage space (280 instead of 250 litres), despite slightly tighter overall dimensions. A neat trick to pull off.

Talk me through the new Audi TT Roadster range.

Three engines: first, a frugal, torquey and eager 184bhp 2.0-litre diesel, which is manual and front-drive only. In contrast, there’s the 230bhp 2.0 TFSI petrol, which can be had with quattro and the six-speed dual-clutch S-tronic transmission. Next on the power ladder is this one, the 310bhp TTS quattro Roadster, which comes with a manual box if you really insist.

Due late next year, the even brawnier TTRS featuring a new alloy-block 2.5-litre five-cylinder engine rated at 460bhp will not only challenge the Boxster GTS but most likely also the 911 cabriolet.

Although the TTS feels substantially faster than the base model, the numeric differences are relatively marginal. From 0-62mph, the S version eclipses the TFSI by 4.9 against 5.6sec, but the top speed is an identical 155mph, the torque duel (280 against 273lb ft) is virtually a dead heat, and the same applies to the fuel consumption (more or less 41 vs 42mpg).

How good is the Audi TT Roadster at being a convertible?

Not bad at all. Pick from black, grey or beige for the powered soft-top, which takes only ten seconds to open and close and can do so while the car’s travelling at up to 30mph. Handily, the snug-fitting and well insulated five-layer fabric hood doesn’t impair the cargo volume when in let-the-sunshine-in position. The extra-cost electric wind deflector and neck warmer may be scoffed at by purists, but like the seat heaters they’re must-haves for winter driving with the top down.

Prominent fixed rollover hoops tower behind the head restraints, and behind them, like the coupé, there’s a rear spoiler that extends above 75mph to increase downforce and enhance directional stability.

Is the TTS version better to drive than the regular TT Roadster?

It does feel more energetic. Wider wheels, tauter springs and magnetically controlled dampers, higher boost pressure, and a more pronounced willingness to rev (redline’s at 6800rpm) help, as do the switchable quad-tailpipe exhaust and sound actuator, which fills the cabin with a sonorous full-bore roar.

The S-tronic gearbox is not only very good at passing on maximum momentum with minimum intermission, but also puts a smile on your face when it blips the throttle for downshifts in dynamic mode. Use the fingertip paddles for best results: much more accurate, and so much more involving.

While the bottom three ratios are spaced for a brisk take-off performance and early acceleration urge, sixth gear is a stress-reducing overdrive. Fourth feels ideal for long 70mph-plus sweepers, fifth equals attack mode on the autobahn.

Do we miss the manual box and front-wheel drive? We certainly don´t.

Does it handle?

There’s all kind of electronic witchcraft at work in quattro four-wheel drive models, momentarily decelerating the wheels closest to the apex to support the turn-in motion and reduce understeer. In Sport mode, torque is shifted to the rear diff as soon as the driver flicks the helm. Keep the loud pedal depressed and it’ll even push into a moderate drift which can be held, with a bit of luck, until the exit of the bend where the front wheels pull the car straight again.

Still not enough drama? Then switch off ESC altogether - but beware: on slippery tarmac you must now brace yourself for lurid lift-off oversteer, for a sudden loss of cornering grip at either end, and for a fair amount of wind-up and shock as the forces play havoc with each other.

On dry roads you rarely experience any deflection of the flight path at all. Instead, this cute two-seater behaves like a fast and totally unfazed monorail cab which stays on course no matter what, at least until the tyres get hot.

Although Audi is offering 19- and 20-inch wheels along with an S-line suspension, softies like me are happy with the standard 18-inchers and with the magnetic ride in Comfort mode.

Verdict

The TT and TTS roadster may not take your breath away, but it is notably more involving than the SLK, far more practical than the overweight Z4 and more attractively priced than the Boxster. In addition, it’s more of a trend-setter than all of them in terms of ergonomics, infotainment and hewn-from-solid build quality.

At the end of the day, the Audi would probably succumb to the Porsche in terms of raw driving pleasure and emotion. But it very probably is the quickest of the lot from A to B, and it might be the only sporty soft-top you could live with 24/7, 365 days a year.